[MDEV-12200] Query Cache Contention Created: 2017-03-07  Updated: 2022-11-01  Resolved: 2022-11-01

Status: Closed
Project: MariaDB Server
Component/s: Query Cache
Affects Version/s: 10.0.29-galera
Fix Version/s: N/A

Type: Bug Priority: Major
Reporter: Suresh Srinivas Assignee: Oleksandr Byelkin
Resolution: Duplicate Votes: 0
Labels: performance
Environment:

Operating System
Distributor ID: Ubuntu
Description: Ubuntu 16.04.1 LTS
Release: 16.04
Codename: xenial

CPU:
Broadwell EP - Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz with HT and Turbo ON.

Running HHVM with Wordpress to talk to the database


Issue Links:
Duplicate
duplicates MDEV-18764 Query cache lock contention Open

 Description   

oss-performance is a Hack language script which controls the operation of nginx, siege, and a specified PHP or HHVM runtime using MariaDB.

It performs the following steps:
Installs the workload (from an included archive)
Starts nginx, Initializes the PHP engine, Performs a sanity check
Runs 200 sequential requests with siege (single threaded warmup)
Runs siege for a 60 second multi-threaded warmup
Benchmarks with siege for 60 seconds of multi-threaded access
Tears down nginx and PHP
Prints results
Install from link OSS-performance

When the Query Cache is enabled, we see very low CPU utilization and in the mariadb shell we see (using show processlist that they are waiting on the query cache.

We disabled the Query Cache and are able to saturate the CPU and also doubled the performance.



 Comments   
Comment by Elena Stepanova [ 2017-03-08 ]

sanja, please take a look. I didn't try to reproduce yet.

Comment by Alexander Krizhanovsky (Inactive) [ 2019-04-11 ]

The contention is easy to reproduce. I described technical issues and a proposal to rewrite QC in MDEV-18764, but there are opinions to remove QC at all, just like Oracle did this.

Comment by Oleksandr Byelkin [ 2019-10-11 ]

you can switch it off if you want

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